1. Field of the Invention
The present invention relates to a needle roller bearing, a retainer of the needle roller bearing and their manufacturing methods. Furthermore, the present invention relates to various kinds of structures comprising the needle roller bearing.
2. Description of the Background Art
A 2-cycle engine having a small engine capacity is used in a utility engine in an agricultural machine and the like. A technique regarding such 2-cycle engine is disclosed in Japanese Unexamined Patent Publication No. 7-332371.
FIG. 14 is a longitudinal sectional view showing a 2-cycle engine using needle roller bearings at a small end part and a large end part of a connecting rod. Referring to FIG. 14, the 2-cycle engine comprises a crankshaft 103 that outputs a rotary motion, a piston 105 that conducts a linear reciprocating movement by means of combustion of mixture gas, and a connecting rod 104 connecting the crankshaft 103 to the piston 105 to convert the linear reciprocating motion to the rotary motion. The crankshaft 103 rotates around a rotation center shaft 111 and a balance weight 112 maintains the rotation balance.
The connecting rod 104 comprises a large end part 115 at a lower part of a linear rod body and a small end part 116 at an upper part thereof. The crankshaft 103 is rotatably supported by the large end part 115 of the connecting rod 104 and a piston pin 114 connecting the piston 105 to the connecting rod 104 is rotatably supported by the small end part 116 of the connecting rod 104 through each roller bearing 106.
A mixture of gasoline and lubrication oil is sent from an inlet 107 to a crank chamber 102 and then sent to a combustion chamber 109 provided above a cylinder 101 according to a vertical movement of the piston 105 and burned. Exhaust gas after burning is exhausted from an outlet 108.
A shell type needle roller bearing which can receive high load and has highly rigidity in spite of its small bearing projected area is used as the above roller bearings which are provided at the small end part and the large end part of the connecting rod and support the piston pin and the crankshaft. Here, the shell type needle roller bearing comprises a shell type outer ring formed by processing a steel plate in a drawing process and the like, needle rollers, and a retainer arranged along an inner diameter surface of the shell type outer ring. Pockets for holding the needle rollers are provided in the retainer and pillar parts positioned between the adjacent pockets retain intervals of the needle rollers.
Here, a manufacturing method of the retainer contained in the above shell type needle roller bearing will be briefly described. First, a band steel which is a material of the retainer is punched out to form pocket holes having a size in which the rollers can be held. Then, the band steel is pressed so that its sectional configuration may be in the form of a V shape. After the pressing process, it is cut to a length that is equal to a circumferential length of the retainer, the cut band steel is bent and formed into a cylindrical shape, end surfaces of the bent steel plate are bonded by welding and the like, and a heat treatment process is performed for it, whereby the retainer is manufactured.
Here, when the band steel is pressed to be formed into the V shape in section, since a sectional height in a diameter direction can be ensured, the following effect is provided. FIGS. 15A and 15B are sectional views showing the band steel in the diameter direction before and after the band steel is formed into the cylindrical shape after the pressing and cutting processes, respectively. Since an interval of pillar parts 126 on an inner diameter surface 132 before the retainer is formed into the cylindrical shape (FIG. 15A) becomes small after the retainer is formed into the cylindrical shape (FIG. 15B), a needle roller 123 retained in the pocket can be prevented from falling off toward the inner diameter surface 132. In this case, when a component to prevent the roller from escaping is further provided on the side of an outer diameter surface 131 of the pillar part 126, the needle roller 123 is prevented from escaping toward the outer diameter surface 131.
In addition, FIG. 16 is a view showing a state in which a retainer 124 retaining the needle rollers 123 is incorporated in an outer ring 122 and a shaft 121. By the pressing process performed to form the sectional configuration into the V shape, the needle roller 123 can be guided in the vicinity of a PCD (Pitch Circle Diameter) 125 in which the movement of the needle roller 123 can be most stably controlled.
In addition, a retainer of a needle roller bearing having the same configuration as that of the retainer manufactured by the above steps is disclosed in Japanese Unexamined Patent Publication 2005-98368.
In the above pocket punching-out process, the material of the retainer is punched out by a punch having a punching blade such that a pocket configuration is pressed with the blade and punched out. At this time, in a sidewall surface of the punched pocket, that is, a sidewall surface of the pillar part positioned between the pockets, a sheared surface and a fractured surface are generated. The sheared surface is a flat and smooth surface punched out with the punching blade of the punch and the like, and the fractured surface is a rough surface fractured by a material pressed by the blade.
Here, in the pocket punching-out process, when the pocket is punched out from the side which becomes an inner diameter surface when the material is formed into the cylindrical shape, the fractured surface is positioned on the side which becomes the outer diameter surface of the sidewall surface of the pillar part.
FIG. 17 is a sectional view showing the retainer 124 in a diameter direction in the above case, and FIG. 18 is a sectional view of the retainer in an axial direction in the above case. In FIG. 18, a part surrounded by a dotted line is the needle roller 123 held in the pocket of the retainer 124 and a one-dot chain line shows the PCD 125. Referring to FIGS. 17 and 18, when the pocket is punched out from a direction of an arrow X in the drawings, which is the side of the inner diameter surface 132, a sheared surface 128 is formed on the side of the inner diameter surface 132 of a sidewall surface 130 and a fractured surface 129 is formed on the side of the outer diameter surface 131 of the sidewall surface 130. Here, since the retainer 124 is pressed into the V shape in section, when the needle roller 123 is held therein, the fractured surface 129 is positioned in the center part of the sidewall surface 130 in the vicinity of the PCD 125, and the sheared surface 128 is positioned at ends of the sidewall surface 130 in the vicinity of the PCD 125.
A configuration curve 134 of the sidewall surface 130 along the PCD 125 in this case is shown in FIG. 19 together with an outline 133 of the needle roller 123. Referring to FIG. 19, the center of the sidewall surface 130 is the fractured surface 129 and end parts thereof are the sheared surface 128. Thus, the configuration curve 134 is recessed to the center part with respect to the outline 133, so that the needle roller 123 is in contact with the sheared surface 128 at the end parts of the sidewall surface 130 when guided.
However, since the end part of the needle roller 123 is a chamfered part and the end part of the sidewall surface 130 does not have a configuration to follow the outline 133 of the needle roller 123, they cannot be appropriately in contact with each other, so that the needle roller 123 cannot be stably guided. When the roller bearing comprising such retainer is used in the piston pin supporting structure of the 2-cycle engine and the like, the roller is skewed and seizing could occur.
A shell type roller bearing for a laminated connecting rod has the similar problems.
The connecting rod used in the engine is manufactured by forging, sintering or restraint pressure forming a steel rod material or a plate material. As another method, the connecting rod is punched out from a steel plate by a pressing process. When the connecting rod is manufactured by the forging or sintering process, since many manufacturing steps are required, it is difficult to reduce its cost. Furthermore, when a hole and the like is formed in the connecting rod, since a grinding process and the like is to be performed, the number of steps is further increased.
As a connecting rod assembly which can be easily and inexpensively manufactured, prevent a bearing and the like to be set in a large end part or a small end part from being skewed, and improve bending strength and buckling strength, there is proposed an assembly in which connecting rod division parts having a large end part, a small end part and a rod part individually are laminated and the laminated connecting rod division parts are integrally fixed so that the adjacent connecting rod division parts are connected by engaging a connecting projection formed in the rod part by a pressing process with a recess formed on a back surface of the projection or with a through hole formed separately from the projection (Japanese Unexamined Patent Publication No. 2004-324760, for example).
According to this construction, since the connecting rod division parts are laminated, even when an inner diameter surface of the large end part or the small end part of the connecting rod division part is skewed, the skew of an inner diameter surface of a large end or a small end of the laminated connecting rod can be eliminated. For example, when each of the connecting rod division parts is normally pressed out, the large end part or the small end part of each connecting rod division part is skewed because of its fractured surface. However, since each thickness is small because of division, a level difference between a sheared surface and a fractured surface is small, and fractured surfaces are dispersed when laminated. Thus, the skew of the inner diameter surface of the large end or the small end of the laminated body can be eliminated as a whole. Therefore, when the shell type roller bearings are press fitted in the large end and the small end, the outer ring is not skewed. Thus, since each of the connecting rod division parts can be pressed out, it is not necessary to perform a post-process such as grinding or polishing for the large end part and the small end part. Thus, the connecting rod assembly can be manufactured easily and inexpensively.
Furthermore, since the laminated connecting rod division parts are connected by engaging the projection pressed in the rod part with the recess formed on the back surface of the projection, or with the through hole formed separately from the projection, they can be rigidly connected. Since the laminated connecting rod division parts are connected by means of the projection and the recess and the like at the rod part, bending strength and buckling strength at the rod part are improved. Since the projection and the recess formed on the back surface thereof are provided by the pressing process, they can be easily formed.
As a bearing in this connecting rod assembly, the shell type roller bearing comprising the shell type outer ring formed by the pressing process including the drawing step, the plurality of needle rollers arranged along the inner diameter surface of the outer ring, and the retainer retaining these needle rollers can be employed. The conventional shell type needle roller bearing has problems described with reference to FIGS. 15 to 19.